1. Field of the Invention
This invention relates to improvements in local area network adapters.
2. Background Art
A local area network (LAN) is a high bandwidth computer network, operating over an area, such as an office or a group of offices. In order for individual computers to communicate with others or with a host or server each computer must have a LAN adapter.
Two styles of LAN adapter have emerged due to the predominance of Ethernet and Token-Ring networks. The Ethernet MAC protocol requires no local processing, so Ethernet adapters tend to be simple "dumb" adapters. The Token-Ring protocol requires local processing of MAC frames by the adapter, so Token-Ring adapters need a local CPU, making them "smart" adapters. These smart adapters usually use some form of "store and forward" architectiure due to the need for local processing. Storage may, for example, be provided by a random access memory (RAM) array.
Fragmentation of data is a feature of many LAN protocols and accordingly there is a need for LAN adapters to be capable of fragmenting data preferably into arbitrary byte length fragments starting on any byte address.
In some protocols, frames are created from, for example, as many as ten separate fragments. Fragments which may be any number of bytes long are not guaranteed to start on a word boundary and of course the word boundary itself is determined by the system.
Advanced buses such as PCI (Peripheral Component Interconnect), stream data as bursts of word transfers (32 bit on PCI). Fully utilizing the bandwidth possible on such buses and meeting the fragmentation requirements of LAN protocols stacks is a challenging problem.